All forms of life need iron, but in particular, bacteria cannot grow unless they have a source of iron to draw from in the environment. The human body and its immune system actually restrict iron levels to keep bacterial growth in check; however, some pathogenic bacteria have found a way around the immune system by secreting siderophores, small molecules that bind and sequester iron from the environment and carry it back to the bacteria. These bacteria also have a receptor that binds to the siderophore, which brings the iron inside, passing through its membranes to the cytoplasm, so it can be used in a number of critical chemical reactions that keep the bacteria functioning and growing. Therefore, if the iron can be taken out of the body with a chelator (which acts like a sponge for iron), the bacteria will be more susceptible to antibiotics because they are in a stressed condition.